Swift 4 - 如何从数组中返回重复值的计数？ [复制]

Question

我有一个包含多个值（双精度值）的数组，其中许多是重复值。我想返回或打印所有唯一值的列表，以及给定值在数组中出现的次数。我对 Swift 很陌生，我尝试了几种不同的方法，但我不确定实现这一目标的最佳方法。

类似这样的： [65.0, 65.0, 65.0, 55.5, 55.5, 30.25, 30.25, 27.5]

将打印（例如）： “65.0 时 3 个，55.5 时 2 个，30.25 时 2 个，27.5 时 1 个。”

我真正关心的不是输出，而是实现这一点的方法。

谢谢！

Answer 1

正如@rmaddy 已经评论的那样，您可以使用Foundation NSCountedSet，如下所示：

import Foundation // or iOS UIKit or macOS Cocoa

let values = [65.0, 65.0, 65.0, 55.5, 55.5, 30.25, 30.25, 27.5]
let countedSet = NSCountedSet(array: values)
print(countedSet.count(for: 65.0))   // 3
for value in countedSet {
    print("Element:", value, "count:", countedSet.count(for: value))
}

---

Xcode 11 • Swift 5.1

您还可以扩展 NSCountedSet 以返回元组数组或字典：

extension NSCountedSet {
    var occurences: [(object: Any, count: Int)] { map { ($0, count(for: $0))} }
    var dictionary: [AnyHashable: Int] {
        reduce(into: [:]) {
            guard let key = $1 as? AnyHashable else { return }
            $0[key] = count(for: key)
        }
    }
}

---

let values = [65.0, 65.0, 65.0, 55.5, 55.5, 30.25, 30.25, 27.5]
let countedSet = NSCountedSet(array: values)
for (key, value) in countedSet.dictionary {
    print("Element:", key, "count:", value)
}

对于 Swift 原生解决方案，我们可以扩展 Sequence，将其元素限制为 Hashable：

extension Sequence where Element: Hashable {
    var frequency: [Element: Int] { reduce(into: [:]) { $0[$1, default: 0] += 1 } }
}

---

let values = [65.0, 65.0, 65.0, 55.5, 55.5, 30.25, 30.25, 27.5]
let frequency = values.frequency
frequency[65] // 3
for (key, value) in frequency {
    print("Element:", key, "count:", value)
}

---

那些会打印出来的

Element: 27.5 count: 1
Element: 30.25 count: 2
Element: 55.5 count: 2
Element: 65 count: 3

Answer 2

您可以枚举数组并将值添加到字典中。

var array: [CGFloat] =  [65.0, 65.0, 65.0, 55.5, 55.5, 30.25, 30.25, 27.5]
var dictionary = [CGFloat: Int]()

for item in array {
   dictionary[item] = dictionary[item] ?? 0 + 1
}

print(dictionary)

或者你可以在数组上做foreach：

array.forEach { (item) in
  dictionary[item] = dictionary[item] ?? 0 + 1
}

print(dictionary)

或者正如@rmaddy所说：

var set: NSCountedSet =  [65.0, 65.0, 65.0, 55.5, 55.5, 30.25, 30.25, 27.5]
var dictionary = [Float: Int]()
set.forEach { (item) in
  dictionary[item as! Float] = set.count(for: item)
}

print(dictionary)